Vehicle wipers have a wiper arm that is swept back and forth over the windshield, carrying the wiper blade with it. A tension spring biases the arm and blade down continually, toward the windshield, so as to maintain a constant wiping pressure. Some mechanism is necessary to physically mount the blade to the arm, preferably in such a way that the blade can be removed and replaced. Ideally, the same mechanism would also evenly distribute the arm pressure to the blade while allowing the blade to conform to the curve of the windshield. Most production wipers today use a blade mount that consists of a series of interpivoted yokes, which support the blade at a number of locations evenly spaced along its length. This distributes pressure evenly, but still allows the blade to conform.
If the blade is mounted beneath the arm with such a mechanism, a good deal of vertical space is required, giving the wiper a large height or profile. This may be objectionable from a styling standpoint, or because of air drag. An alternative is to mount the blade to the side of the arm, with a similar mechanism. Side mounted blades offer a significantly lower height profile above the windshield, but obviously occupy more side to side or lateral area over the windshield. This, too, may be objectionable from a styling standpoint.